Guard time optimisation and adaptation for energy efficient multi-hop TSCH networks

International audienceIn the IEEE 802.15.4-2015 standard, Time Slotted Channel Hopping (TSCH) aims to guarantee high-level network reliability by keeping nodes time-synchronised. In order to ensure successful communication between a sender and a receiver, the latter starts listening shortly before the expected time of a MAC layer frame's arrival. The offset between the time a node starts listening and the estimated time of frame arrival is called guard time and it aims to reduce the probability of missed frames due to clock drift. In this paper, we investigate the impact of the guard time on network performance. We identify that, when using the 6tisch minimal schedule, the most significant cause of energy consumption is idle listening during guard time. Therefore, we first perform mathematical modelling on a TSCH link to identify the guard time that maximises the energy-efficiency of the TSCH network in single hop topology. We then continue in multi-hop network, where we empirically adapt the guard time locally at each node depending its distance, in terms of hops, from the sink. Our performance evaluation results, conducted using the Contiki OS, demonstrate that the proposed decentralised guard time adaptation can reduce the energy consumption by up to 40%, without compromising network reliability

Otimização da eficiência energética em redes operando com tsch: avaliação analítica de uma implementação prática.

The IEEE 802.15.4-2015 standard defines a number of Medium Access Control (MAC) layer protocols for low power wireless communications, which is desirable for constrained Internet of Things (IoT) devices. Originally defined in IEEE 802.15.4e amendment, the Time Slotted Channel Hopping (TSCH) is recently attracting the attention from the research community, due to its reduced contention (time scheduling) and robustness (channel hopping). However, the TSCH needs a certain level of synchronization between the nodes, which can lead to a higher energy consumption. A guard time mechanism is implemented to ensure that the nodes will hear the frames even if they are not perfectly synchronized. In this work, we implement the Guard Beacon strategy, aiming to reduce the guard time, and present a realistic energy consumption model for a Contiki OS-based TSCH networks. The analytical values have a good match with the results obtained from the Contiki Powertrace Tool running on a real TSCH network and demonstrate that the proposed scheme can reduce the overall power consumption of each node by 13.05%.O padrão IEEE 802.15.4-2015 define novos protocolos para a camada de acesso ao meio (MAC, do inglês Medium Access Control) com foco em redes de comunicação sem fio com baixo consumo de energia, o que é desejável para dispositivos de Internet das Coisas (IoT, do inglês Internet of Things) que apresentam restrições energéticas. Originalmente definido na emenda IEEE 802.15.4e, o esquema de Salto de Canais por Intervalo de Tempo (TSCH, do inglês Time Slotted Channel Hopping) tem atraído atenção da comunidade científica devido ao nível reduzido de contenção (agendamento no tempo) e robustez (salto de canais). Entretanto, para operar corretamente o TSCH necessita de um determinado nível de sincronização entre os nós da rede, o que pode levar a um maior consumo de energia. Um mecanismo de tempo de guarda é implementado para assegurar que os nós irão “ouvir” os pacotes ainda que não estejam perfeitamente sincronizados. Neste trabalho, implementa-se a estratégia de Guard Beacon visando reduzir o tempo de guarda necessário, e se apresenta um modelo de consumo de energia realista para redes operando com TSCH e Sistema Operacional Contiki. Os resultados analíticos têm boa precisão quando comparados com os resultados obtidos de uma rede TSCH real através da ferramenta Powertrace do Contiki e demonstram que o esquema proposto pode reduzir o consumo de energia geral de cada nó em até 13,05%

Adaptive Compensation for Time-Slotted Synchronization in Wireless Sensor Network

Since time division multiple access (TDMA) is employed to reduce power consumption, time synchronization is critically important for wireless sensor networks. Packet-based clock correction is one of main methods to maintain synchronization among nodes. However, in many real cases, such as industrial equipment monitoring and diagnosis, there is no need to exchange messages during relatively long time, while highly accurate time synchronization has to be maintained, which results in that additional packets have to be exchanged specifically for synchronization purpose. For addressing this problem, an adaptive compensation method is proposed in this paper to achieve a high synchronization precision without exchanging message frequently. We proved that the adaptive compensation method can achieve a high synchronization precision with much fewer packet exchanges. In addition, the performance of the proposed scheme has been evaluated in three different experimental settings. In the indoor experiment, compared with the synchronization method without using compensation, 98% of the synchronizing packets can be eliminated while maintaining synchronization precision at 100  μ s. In the outdoor experiment with higher temperature fluctuation, 80% of the packets can be eliminated with 100  μ s synchronization precision. In the case of sudden temperature changes of more than 10 ° C, the proposed compensation packet frequency regresses to the frequency of the synchronization method without compensation

Zeitsynchronisation in drahtgebundenen Rechnernetzen

Ausgehend von einer Analyse des Standes der Technik werden neuartige Verfahren für die Zeitsynchronisation in drahtgebundenen Netzwerken vorgestellt. Unter anderem wird, zum ersten Mal im Bereich der Zeitsynchronisation, eine Kombination aus Linearer Optimierung und Broadcast-Nachrichten vorgestellt, was eine Verbindung der jeweiligen Genauigkeits- und Skalierbarkeitsvorteile ermöglicht. Weiterhin wird, ebenfalls zum ersten Mal im Bereich der Zeitsynchronisation, eine Kombination aus Linearer Optimierung und Temperaturkompensation vorgestellt.Based on an analysis of the state of the art, several new time synchronization methods for wired networks are proposed. Among others, for the first time in the synchronization domain, a combination of linear programming and broadcast messages is proposed, which allows combining the respective accuracy and scalability advantages. Moreover, this thesis proposes combining linear programming and temperature compensation, also for the first time in the field of time synchronization